The present invention concerns a watch with a mechanical movement and it relates to the reduction of rate variations which result from the effects of gravity on the regulating members of the watch, because of inevitable faults in the poising of such members, and because of the variation of these effects in the various positions that the user imposes on his or her watch.
The tourbillon invented two centuries ago by Abraham-Louis Breguet is a device that causes such a reduction. As the oscillator and the escapement are mounted in a carriage that rotates about an axis parallel to the axis of the sprung balance assembly, the gravity component that is exerted in the plane perpendicular to these axes performs a continuous rotation in relation to the members, such that each rotation of the carriage leads to a compensation of the effects of any disequilibrium in that plane and thus improves the regularity of rate of the watch when it is worn, especially when the watch is in a vertical or inclined position. In order to simplify the terminology, the term “tourbillon” is used here to designate both devices in which the balance axis coincides with the axis of rotation of the carriage (for example in accordance with Breguet or in accordance with CH Patent No. 262 017) and the devices that are often called “carrousels”, when such axes are distinct (see for example CH Patent Nos. 30 754, 256 590 and EP Patent No. 846 987).
Given that a conventional tourbillon does not compensate perfectly for the effects of gravity, watchmakers looking to further improve the isochronism of high quality mechanical watches have devised tourbillons with two or three axes of rotation perpendicular to each other, disclosed in particular in Patent Nos. GB 2 027 232, CH 693 832, EP 1 465 024 and WO 2004/077171. These designs constitute remarkable technical prowess, but they occupy a spherical space and thus can only be placed in an extremely thick watch.
According to WO Patent No. 03/017009, a similar object is achieved by means of a tourbillon with two axes of rotation which intersect at an angle other than 90°, for example at 30°. This design is more compact in height than that with two perpendicular axes, but it remains considerably thicker than a conventional tourbillon movement.
FR Patent No. 2 784 203 presents yet another manner of reinforcing the compensation produced by the tourbillon. The tourbillon, the barrel that drives it and the gear train connecting these two elements are all mounted on a rotating plate completing one revolution per hour, whose axis of rotation is parallel to that of the tourbillon. This arrangement forms, in a way, a tourbillon on a carrousel, with the tourbillon completing revolutions about the centre of the rotating plate.
Another idea, consisting in coupling two regulating members mounted on the plate of a watch movement in order to average their rate by means of a differential gear, was formulated in the 1930s by Mr. Vuilleumier and published in CH Patent No. 156 801, but this concerned only the usual stationary regulating systems (sprung balance and escapement). An improvement consisting in mounting such an assembly on a rotating plate is disclosed in the work of R. Meis “Le Tourbillon”, ISBN 2-85917-097-9, Editions de I'Amateur, Paris, 1990, p. 75-77, but it remains at the model stage, and has not been able to be integrated into a watch.